Oscillators comprise a resonator having a resonant frequency that can change due to environmental factors, such as temperature and contaminants that deposit on the surface of the resonator. The ability to measure changes in the resonant frequency of the resonator allows for many types of measurements to be made. Illustratively, changes in the resonant frequency due to the presence of a harmful contaminant in the ambient, or changes in the resonant frequency due to changes in temperature, can be the basis of a device for detecting harmful contaminants, or the basis of a thermometer.
Thermometers can measure changes in temperature at a particular location through measurements of changes in a resonant frequency of the resonator of the oscillator. In a typical thermometer, a first resonator is a component of a first oscillator and a second resonator is a component of second oscillator. The first resonator (“measurement resonator”) is disposed adjacent to an object or element under measurement, and the second resonator (“reference resonator”) is disposed far enough away from the measurement site that changes in the temperature of the object do not impact its resonant frequency. In order to account for common mode heating effects from the ambient, the resonant frequency of the reference resonator is measured at the same times as the measurement resonator, and is subtracted from the frequency of the reaction resonator.
Thermometers are used, for example, to measure a change in temperature caused by a chemical reaction of a sample. Because of the temperature dependence of the resonator of the oscillator, a change in temperature causes a change in the resonant frequency of the reaction resonator. As such, the thermometer tracks the frequency of the oscillator versus time during the reaction, and the change in temperature of the measurement site is determined based on previous characterization of the change in resonant frequency versus temperature.
Typically in thermometers, determination of the temperature over time involves placement of a large number of pairs (measurement and reference) of oscillators near respective reaction sites. Each oscillator generates a unique frequency, and each frequency output from each oscillator is transported away from the thermometer array (e.g., on coaxial cables) to a large number (e.g., hundreds) of remote frequency counters. The subtraction of the reference frequency from the reaction frequency is then made and the difference between the reaction temperature and the reference temperature is determined algorithmically, for example, in a processor.
Unfortunately, a thermometer incorporating such a large number of frequency counters is not only complex, but also comparatively expensive. Furthermore, the accuracy of such a thermometer can be diminished due to thermal leaks that can occur between the oscillators and their respective frequency counters. Additionally, such an implementation is susceptible to inaccuracies due to cross-talk between oscillators.
What is needed, therefore, is an apparatus and a method for measuring a change in the frequency of an oscillator that overcomes at least the shortcomings of known apparatuses such as those described above.